Both Sen. John F. Kerry (D-Mass.), left, and Sen. John McCain (R. Ariz.) have championed the issue of global warming for years. But, for the moment, McCain is barely engaged in the issue while Kerry has emerged as a major dealmaker.
(By Mary Schwalm -- Associated Press)

As climate change reemerges as an issue in the national policy debate, it may help define the legislative legacies of two men who once vied for the White House: Sens. John F. Kerry (D-Mass.) and John McCain (R-Ariz.).

Both men have championed the issue of global warming for years, including when they served as their party's presidential nominees in 2004 and 2008, respectively. But, for the moment, McCain is barely engaged in the issue beyond criticizing the climate bill passed by the House, while Kerry has emerged as one of the chamber's leading dealmakers. The fact that the two no longer appear to be on the same side underscores the challenge Democrats face in enacting the first national cap on greenhouse gas emissions.

"This is a tough lift, in every respect," said Kerry, who has held 40 one-on-one meetings with 25 fellow Democrats over the past couple of months and plans to meet with half a dozen Republicans in the next week or so. "My hope is that common sense and the facts will prevail, but that doesn't always happen around here."

With health care dominating the Senate's agenda, climate change largely receded from public view this summer. Now Democratic leaders want to make enough progress to provide U.N. negotiators meeting in December in Copenhagen with a clear sense of the U.S. position on global warming, but many centrist Democrats and most Republicans remain deeply skeptical of whether the Senate can pass legislation by then.

Kerry aims to unveil the bill that he has been working on with Sen. Barbara Boxer (D-Calif.), chairman of the environment committee, by the end of the month. He said he and others have been trying to gauge what compromises are needed to pass a bill that would cap the nation's greenhouse gas emissions and allow companies to buy and sell pollution credits. "It's more important to get started than being rigid about your starting point," he said.

But several key senators, including McCain, have questioned whether the bill will be conservative enough to muster the needed votes. Sen. Joseph I. Lieberman (I-Conn.), who wrote the Senate's first cap-and-trade measure in 2003 along with McCain, has conferred with Kerry and Boxer but plans to amend whatever they produce in order to garner additional support.

"I'm willing to bend, and I'm asking people to bend," said Lieberman, who is working on issues such as additional subsidies for nuclear and coal power as well as money to ease the economic crunch for utilities and consumers. "I'm willing to meet people in the middle of the bridge because this problem is so urgent."

But Lieberman's name will not be on the main Senate climate bill, and neither will McCain's. McCain has spent much of the past several weeks criticizing the cap-and-trade bill passed in the House, saying on Twitter that it "appears to be a cap & tax bill that I won't support" and telling ABC's "This Week" last month that it had "a lot of special deals for a lot of special interests."

McCain spokeswoman Brooke Buchanan said the senator still has substantive reservations about the emerging proposal in the Senate -- that it lacks sufficient nuclear power subsidies, that the money needs to go to clean-energy research and development rather than general revenue -- as well as procedural ones.

"We have yet to see bipartisan talk on any issue, let alone energy," Buchanan said, adding that the senator is still waiting for a concrete proposal from the administration. "The administration's got to lead. He can't carry the flag on his own."

Carol M. Browner, who directs the White House Office of Energy and Climate Change Policy, said the administration has "done dozens and dozens of meetings up on the Hill" and is confident it can enlist the support of McCain and some of his GOP colleagues.

"My sense is there is a bipartisan opportunity here, without a doubt," said Browner, who has met with McCain. "We would welcome his engagement and would hope to work together on this."

Although both sides in the climate debate see McCain as essential to bringing along a few needed Republicans, some environmental groups have begun to lose patience with him.

"What I suspect is happening is he's stepped into the shadow of partisan politics," said Lexi Shultz, deputy director of the Union of Concerned Scientists' climate program. "He still plays a critical role, and that's because he's one of the few Republicans who knows we can't afford to do nothing. If other Republicans see him sitting on the sidelines, it gives them much more of a pass than they otherwise would have."

McCain has not opted out of the debate altogether. He continues to confer with Lieberman behind the scenes, and late last month he traveled with Sen. Mark Udall (D-Colo.) to see the bark beetle infestation that has plagued Colorado's forests as temperatures have risen there.

"You can't help but be stunned when you see the extent of the bark beetle epidemic," Udall said, adding that he and McCain spoke about how they could "move forward" on issues such as nuclear power. "John sent plenty of signals that climate change is real -- we need to act now for national security reasons as well as for other reasons. And he made it very clear nuclear power needs to be part of it."

Boxer, a longtime foe of nuclear power, said last week that her climate bill will include provisions for the industry. But she and Kerry have an array of Democratic senators they must satisfy as well. Keith McCoy, who as vice president of energy and resources policy at the National Association of Manufacturers has been targeting Democratic Senate offices all summer, said there is "a real struggle" to see whether the bill can help energy-intensive businesses cope with a price on carbon.

Blanche Lincoln (D-Ark.), who took the helm of the Agriculture Committee last week, is concerned about how the bill will treat farmers and foresters who hope to earn money sequestering carbon, as well as middle-income Americans who could face higher electricity prices. Arlen Specter (D-Pa.) is worried about lost manufacturing and coal jobs. And Evan Bayh (D-Ind.) maintains that any bill must ensure that developing nations such as China and India take verifiable steps to cut their emissions if the United States is doing so.

"I think it's going to take time, because it's important to get it right," Lincoln said.

Kerry has met with them all, and he is planning to meet with McCain as well.

"John McCain and I have a long relationship. In recent years, we've been on the opposite sides of a presidential race twice -- mine and his -- but it doesn't alter one iota of my respect for him as a human being," Kerry said. "You've got to reach out to everyone."